The invention relates to a control system for a machine and more particularly to a microprocessor-based control system for a compressor where the operation of the compressor is controlled by an electronic control module which processes actual compressor operating parameter value signals received at regular intervals from compressor sensors, and if one or more of the parameter values is not at a predetermined set point value, the electronic control module generates and transmits signals for modifying operation of the compressor.
Control systems for compressors typically use pneumatically or mechanically actuated devices to control compressor components such as compressor inlet valves. For example, one such control device changes the size of the opening in the inlet valve for modifying the volume of fluid, such as air, supplied to the compressor.
Conventional compressors and their associated control devices are typically designed to operate within an ambient operating temperature range of approximately -20 to 115 F. These conventional compressors generally operate in an efficient manner within the ambient operating temperature range, however, when the compressor is operated outside the ambient operating temperature range, such as in extremely cold or hot conditions, the pneumatically and mechanically actuated control devices described above frequently do not operate as required and the efficiency of the compressor is significantly reduced. Operating the compressor at such reduced efficiency may lessen the life of the compressor bearings, increase noise and vibration produced by the compressor and significantly increase the frequency of repairs. Additionally, the useful life of the compressor may be reduced when using these conventional pneumatically and mechanically actuated compressor control devices.
There are a number of other problems associated with pneumatic and mechanical controls devices. First, such devices have a very large number of discrete component parts which, because such devices rely on fluid flow through the devices, do not operate properly even when the compressor is operated within the designed ambient operating temperature range. In addition, the component parts may stick or freeze in cold temperatures (e.g., near freezing). Also, pneumatic and mechanical control devices have a limited useful life and, over time, the component parts wear out and must be repaired or replaced. As such, the reliability of these conventional control devices is low while the cost to repair and maintain these control devices is high.
One type of compressor includes an oil flooded screw compressor, which introduces oil into a compression module for absorbing at least some of the heat generated during compression. Thus, at high ambient temperatures and full load conditions the amount of oil used should be increased to allow for sufficient cooling. However, at low ambient temperatures and under partial loading conditions, the amount of oil utilized may be lowered because less oil is required for cooling. It is important that the volume of oil utilized be continuously modified as the load capacity of the compression module changes because injecting more oil into the system than necessary will result in excessive power consumption. Thus, although it is highly desirable to inject the exact amount oil required to maintain the temperature of the compressor within a desired range, conventional compressors do not have the capability to modify the flow of oil to obtain optimum performance.
In addition, with conventional compressors, neither the speed of the prime mover nor the position of the compressor inlet valve may be changed independently of one another. In other words, the inlet valve may not be opened or closed without also increasing or decreasing the speed of the prime mover. This rigid interrelation between inlet valve position and prime mover speed limits a compressor operator's ability to obtain the desired compressor discharge pressure.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, It is apparent that it would be advantageous to provide an alternative to thereby overcome one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.